A square is divided into five equal rectangles, each with a circumference of 60 cm and a square with a circumference of () cm A. 300B. 200C. 100

A square is divided into five equal rectangles, each with a circumference of 60 cm and a square with a circumference of () cm A. 300B. 200C. 100

Side length of square: 60 × 5 △ 12 = 300 △ 12 = 25 (CM) perimeter of square: 25 × 4 = 100 (CM) answer: perimeter of square is 100 cm

Given the function f (x) = (x ^ 3-x) / 3, the sequence {an} satisfies A1 > = 1, an + 1 > = f '(an + 1), it is proved that an > = (2 ^ n) - 1
Wrong number. It's f (x) = (x ^ 3 / 3) - X

Certificate:
f'(x)=x²-1
a(n+1)=(an +1)²-1=an²+2an=an(an+2)
If A1 ≥ 1, A1 - (2-1) = A1-1 ≥ 0, the inequality holds
Suppose that when n = K (K ∈ n +), the inequality, that is AK ≥ 2 ^ k - 1, then when n = K + 1,
a(k+1)=ak(ak+2)≥(2^k -1)(2^k -1+2)=2^(2k)-1
k≥1 2k-k≥1 2k≥k+1
a(k+1)≥2^(k+1)-1
The same holds for inequality
In conclusion, an ≥ 2-8319; - 1

The taxi charge standard of a city is as follows: 5 yuan for less than 3 kilometers, and 1 kilometer for more than 3000 meters
If someone wants to travel (x > 3) kilometers
1. Ask for expenses
2. How much is it if he takes 15 kilometers

For each additional kilometer, a yuan will be charged,
1. 7.8km toll: 5 + (7.8-3) a = 5 + 4.8A;
2. It's about X kilometers from Mr. Li's home to the Cultural Palace, obviously x > 3,
5 + (x-3) a = 21.2
The solution is: x = 16.2 / A + 3
You are not qualified for these two questions,
After charging a yuan again, you can directly replace the above two formulas
Please take the answer and support me

Pull the rectangle nailed by 4 pieces of wood into a parallelogram, perimeter (), area ()

Unchanged

Given the quadratic power of X + 3x - 1 = 0, find the quadratic power of 1 / X and (x + 1 / x)

①∵x²+3x-1=0
∴x+3-1/x=0
∴x-1/x=-3
②(1+1/x)²=(1-1/x)²+4
=(-3)²+4
=13

There is a pool filled with water from two pipes. If pipe a is opened only, the pool will be filled in 2 hours and 30 minutes. If pipe B is opened only, the pool will be filled in 5 hours. (1) if pipe a and pipe B are filled with water for 20 minutes at the same time, then pipe B will fill the pool alone. How much time will it take to fill the pool? (2) Suppose that a drainage pipe C is installed under the pool, and a full pool can be drained by opening the C pipe alone for 3 hours. If the three pipes are opened at the same time, how many hours can an empty pool be filled with water?

(1) 2 hours and 30 minutes = 2.5 hours, 20 minutes = 13 hours, [1 - (12.5 + 15) × 13] △ 15, = (1-35 × 13) × 5, = (1-15) × 5, = 4 (hours); (2) 1 △ 12.5 + 15-13, = 1 △ 35-13, = 1 △ 415, = 154 (hours); answer: (1) it will take 4 hours to fill the pool; (2) it will take 154 hours to fill an empty pool

If in the parallelogram ABCD, ab = 8 and the circumference is equal to 24, then ad =?

24/2-8=4

A passenger car and a freight car run in the same direction on parallel tracks. The length of the passenger car is 200 meters, and the length of the freight car is 310 meters. The speed ratio of the passenger car and the freight car is 4:3
A passenger car and a freight car run in the same direction on the parallel track. The length of the passenger car is 200 meters, and the length of the freight car is 280 meters. The speed ratio of the passenger car and the freight car is 5:3. The crossing time for the passenger car to catch up with the freight car is 1 minute. If the two cars run in the same direction, how long is the crossing time?
Please use the equation of first degree in one variable to solve it

If the speed of passenger car is 5 x m / min, the speed of freight car is 3 x m / min
（280+200）÷（5x-3x)=1
2x=480
X = 240, that is, the speed of the bus is 5 × 240 = 1200 (M / min), and the speed of the train is 3 × 240 = 720 (M / min)
If they walk in opposite directions, their crossing time is:
(280 + 200) △ 1200 + 720) = 480 △ 1920 = 0.25 (min)

After a bus arrives in Tianjin, one quarter of the passengers get off and another 300 get on. When driving, the number of passengers on the bus is 90% of that before the bus arrives in Tianjin. How many passengers are there before the bus arrives in Tianjin?

There are x passengers before the train arrives at Tianjin station
3/4x+300=9/10x
3/20x=300
x=2000

Cut the largest circle under a square paper with a circumference of 60 cm. What is the circumference of the circle?

The side length of the square is: 60 △ 4 = 15cm
So the diameter of the largest circle is 15cm
So the perimeter is: π × 15 = 15, π = 47.1cm
Have a good time